The present invention relates to a lighting unit and lighting modules for implementing low-cost display whose display quality is excellent, and a liquid-crystal display using these unit and modules.
Hereinafter, the explanation will be given below concerning a conventional lighting unit and lighting modules, and a liquid-crystal display using these conventional unit and modules.
Up to the present, as displays, a CRT display has been in the mainstream thereof. In recent years, however, an active-matrix liquid-crystal display (which, hereinafter, will be referred to as “LCD”) has been becoming more and more prevalent. The LCD is a display which utilizes light transmittance property of liquid crystal. Namely, the liquid crystal itself emits no light, and performs display by allowing light of a backlight to be transmitted/cutoff. Here, the backlight exists at the rear surface of the liquid crystal.
As most of backlights for this LCD, a fluorescent tube has been used. In recent years, however, there have existed the following reports: Namely, in order to enhance color reproductivity of a displayed image, a light emitting diode (hereinafter, referred to as “LED element”) is used as the backlight. Examples of these reports are as follows: “18.1-inch XGA TFT-LCD with Wide Color Reproduction using High Power LED-Backlighting”, Hideyo Ohtsuki, et al., SID′02 DIGEST, pp. 1154-1157.
The LED element described in this document is a one considerably close to a point light source. As a result, in order to use this LED element as the backlight for a liquid-crystal display for performing flat-surface display, it becomes necessary to assemble the LED elements in plural number and thereby to form a flat-surface light source.
Also, the LED element at present exhibits the following characteristics conspicuously: Namely, in the electric-power-to-light-emission-brightness efficiency (Referred to as light emission efficiency hereafter.), the LED element is lower than the fluorescent tube used so far. Moreover, this light-emission efficiency is lowered by temperature rise.
As a method for solving these problems, there has existed “LED backlight for large area LCD TV's”, Robert Scott West, et al., IDW′03, pp. 657-659. This document indicates an embodiment where large-sized LED elements having an excellent heat-radiation characteristic are positioned in a straight-line-like manner along a few rows.
Also, as an example of the method of forming the flat-surface light source, there has existed JP-A-2002-351342. This document indicates an embodiment where the backlight of the LED elements is configured to be separated into a plurality of regions. Furthermore, there has existed JP-A-2003-156728. This document indicates an example where a diffuser is provided on this flat-surface light source thereby to reduce brightness unevenness which occurs in boundary portions of the flat-surface light source.